1. Field of the Invention
The present invention relates to a radio signal transmitter, related method, and related multimedia system for an audio source generator, and more particularly, to a radio signal transmitter, related method, and related multimedia system for avoiding degradation of audio output quality or influence on other people when receiving broadcasting programs.
2. Description of the Prior Art
Portable multimedia players, such as MP3 (MPEG-1 Audio Layer 3) or CD (Compact Disc) players, etc., can output video and audio signals at any time and in any place. Generally, a portable multimedia player comprises a specific audio output interface for outputting audio signals to an external audio player. For example, an MP3 portable player includes a 3.5 mm audio jack in order to output audio signals to audio output devices, such as speakers or headphones.
Therefore, using the portable multimedia player, a user can enjoy multimedia interaction on the go. However, in some cases, portable multimedia player may not output audio signals through the predetermined output interface. For example, a vehicle multimedia player can be utilized for playing CD, AM, or FM broadcasting programs, etc., but the vehicle multimedia player may not have external interfaces or have improper external interfaces, which do not conform to a format of the use's MP3 player. In other words, the user cannot play audio signals in the MP3 player via the vehicle multimedia player. In such a condition, in order to expand functions of the vehicle multimedia player, the prior art provides an electronic device, which outputs audio signals to the vehicle multimedia player via frequency modulation (FM) channel.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art FM output device 10. The FM output device 10 is installed between an audio source generator 12 and a vehicle multimedia player 14, and utilized for transforming audio signals provided by the audio source generator 12 into FM signals for the vehicle multimedia player 14. The audio source generator 12 can be an MP3 player or a CD player, and comprises an audio generating device 120 and an output interface 122. The audio generating device 120 outputs audio signals to the FM output device 10 via the output interface 122 (e.g. 3.5 mm audio jack). The FM output device 10 includes a receiving interface 100, a modulation unit 102, a transmission antenna 104, and a switching unit 106. The receiving interface 100 can be connected with the output interface 122 for receiving the audio signals provided by the audio source generator 12. The modulation unit 102 is coupled to the receiving interface 100, and utilized for modulating the audio signals into FM signals, so as to emit the FM signals via the transmission antenna 104. The switching unit 106 is utilized for switching frequencies of the FM signals outputted from the modulation unit 102. On the other hand, the vehicle multimedia player 14 includes an audio player device 140, a demodulation unit 142, a reception antenna 144, and a switching unit 146. After the FM output device 10 outputs FM signals via a specific frequency, a user can switch a frequency of the demodulation unit 142 through the switching unit 146, so that the demodulation unit 142 can receive the FM signals provided by the FM output device 10 via reception antenna 144, and demodulate the FM signals. Then, the audio player device 140 can play the demodulated FM signals.
Therefore, using the FM output device 10, the user can adjust the operating frequencies of the modulation unit 102 and the demodulation unit 142 to the same frequency via the switching units 106, 146, so as to play audio signals provided by the audio source generator 12 through the vehicle multimedia player 14. However, such operating approach mentioned above has its limitation; that is, the user must avoid adjusting the operating frequencies of the modulation unit 102 and the demodulation unit 142 to a frequency of a broadcasting program. If the user adjusts the operating frequencies of the modulation unit 102 and the demodulation unit 142 to a frequency of a broadcasting program, signals of the broadcasting program will interfere with the FM signals outputted from the FM output device 10 and affect the output effect of the vehicle multimedia player 14. Meanwhile, the FM signals outputted from the FM output device 10 may affect neighboring vehicle multimedia players when receiving the broadcasting programs. However, there are many broadcasting programs in the air at the same time, and frequencies used by the broadcasting programs may be different in different area, so that the user may easily adjust the operating frequencies of the modulation unit 102 and the demodulation unit 142 to a wrong frequency, i.e. a frequency utilized for a broadcasting program, causing degradation of the audio output quality, or influence on other people when receiving broadcasting programs.
In short, using the prior art FM output device 10, the user blindly chooses the operating frequencies of the modulation unit 102 and the demodulation unit 142 without any reference, leading to degradation of audio output quality, influence on other people when receiving broadcasting programs, as well as inconvenience.